From: Matthew Wilcox (Oracle) willy@infradead.org
commit dcfa24ba68991ab69a48254a18377b45180ae664 upstream.
After we have unlocked the mmap_lock for I/O, the file is pinned, but the VMA is not. Checking this flag after that can be a use-after-free. It's not a terribly interesting use-after-free as it can only read one bit, and it's used to decide whether to read 2MB or 4MB. But it upsets the automated tools and it's generally bad practice anyway, so let's fix it.
Reported-by: syzbot+5b96d55e5b54924c77ad@syzkaller.appspotmail.com Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings") Cc: stable@vger.kernel.org Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/filemap.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
--- a/mm/filemap.c +++ b/mm/filemap.c @@ -2991,11 +2991,12 @@ static struct file *do_sync_mmap_readahe struct address_space *mapping = file->f_mapping; DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff); struct file *fpin = NULL; + unsigned long vm_flags = vmf->vma->vm_flags; unsigned int mmap_miss;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE /* Use the readahead code, even if readahead is disabled */ - if (vmf->vma->vm_flags & VM_HUGEPAGE) { + if (vm_flags & VM_HUGEPAGE) { fpin = maybe_unlock_mmap_for_io(vmf, fpin); ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1); ra->size = HPAGE_PMD_NR; @@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahe * Fetch two PMD folios, so we get the chance to actually * readahead, unless we've been told not to. */ - if (!(vmf->vma->vm_flags & VM_RAND_READ)) + if (!(vm_flags & VM_RAND_READ)) ra->size *= 2; ra->async_size = HPAGE_PMD_NR; page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER); @@ -3012,12 +3013,12 @@ static struct file *do_sync_mmap_readahe #endif
/* If we don't want any read-ahead, don't bother */ - if (vmf->vma->vm_flags & VM_RAND_READ) + if (vm_flags & VM_RAND_READ) return fpin; if (!ra->ra_pages) return fpin;
- if (vmf->vma->vm_flags & VM_SEQ_READ) { + if (vm_flags & VM_SEQ_READ) { fpin = maybe_unlock_mmap_for_io(vmf, fpin); page_cache_sync_ra(&ractl, ra->ra_pages); return fpin;